1. Field of the Invention
The present invention relates to an engine comprising a connecting rod connected at one end to a piston through a piston pin, a first arm turnably connected at one end to the other end of the connecting rod and at the other end to a crankshaft through a crankpin, a second arm integrally connected at one end to the other end of the first arm, a control rod turnably connected at one end to the other end of the second arm, and a movable eccentric shaft mounted between eccentric positions of rotary shafts to which a power reduced at a reduction ratio of 1/2 is transmitted from the crankshaft, the movable eccentric shaft being connected to the other end of the control rod, the stroke of the piston at an expansion stroke being larger than that at a compression stroke.
2. Description of the Related Art
Such engines are conventionally known, for example, from U.S. Pat. No. 4,517,931 and Japanese Patent Application Laid-open No. 9-228853. In each of these engines, the stroke of the piston at an expansion stroke is larger than that at a compression stroke, whereby a larger expansion work is carried out in the same amount of air-fuel mixture drawn, so that the cycle thermal efficiency is enhanced.
In the conventionally known engine, it is common that the position of a top dead center at each of the intake and exhaust strokes and the position of the top dead center at the compression stroke are different from each other. However, if the position of the top dead center at each of the intake and exhaust strokes is higher in level than the position of the top dead center at the compression stroke, there is a possibility that the interference of each of intake and exhaust valves and a top of the piston with each other occurs. If the position of the top dead center at each of the intake and exhaust strokes is lower in level than the position of the top dead center at the compression stroke to avoid the interference, the top dead center at the compression stroke is further lower and hence, an enhancement in a compression ratio in the engine is not desired and it is difficult to operate the engine at a higher thermal efficiency. On the other hand, if the top dead center at the compression stoke is higher in level than the top dead center at each of the intake and exhaust strokes, there is a possibility that the scavenge provided by the piston is insufficient due to the lower level of the piston at the top dead center at each of the intake and exhaust strokes, and thus, a large amount of burned gas remains within a cylinder, thereby bringing about a reduction in output in a full-load state and the instability of burning in a lower-load state.
Accordingly, it is an object of the present invention to provide an engine, wherein the stroke of the piston at the expansion stroke is larger than that at the compression stroke and in addition, the top dead center at each of the intake and exhaust stroke and the top dead center at the compression stroke are at the same level, whereby the above-described problems are solved.
To achieve the above object, according to a first feature of the present invention, there is provided an engine comprising a connecting rod connected at one end to a piston through a piston pin, a first arm turnably connected at one end to the other end of said connecting rod and at the other end to a crankshaft through a crankpin, a second arm integrally connected at one end to the other end of said first arm, a control rod turnably connected at one end to the other end of said second arm, and a movable eccentric shaft mounted between eccentric positions of rotary shafts to which a power reduced at a reduction ratio 1/2 is transmitted from said crankshaft, said movable eccentric shaft being connected to the other end of said control rod, the stroke of said piston at an expansion stroke being larger than that at a compression stroke, wherein when various dimensions are represented as described below in an x-y plane constituted by an x-axis extending through an axis of said crankshaft along a cylinder axis and a y-axis extending through the axis of said crankshaft in a direction perpendicular to the x-axis: a length of said connecting rod is represented by L4; a length of said first arm is represented by L2; a length of said second arm is represented by L1; a length of said control rod is represented by L3; a length from the axis of said crankshaft to axes of said rotary shafts in a direction of the y-axis is represented by L5; a length from the axis of said crankshaft to the axes of said rotary shafts in a direction of the x-axis is represented by L6; an angle formed by said connecting rod with respective to the cylinder axis is represented by xcfx864; an angle formed by said first and second arm is represented by a; an angle formed by said second arm with the y-axis within the x-y plane is represented by xcfx861; an angle formed by said control rod with the y-axis is represented by xcfx863; an angle formed by a straight line connecting the axis of said crankshaft and said crankpin with the x-axis is represented by xcex8; an angle formed by a straight line connecting the axes of said rotary shafts and the axis of said movable eccentric shaft with the x-axis is represented by xcex8p; a value of the angle xcex8p is represented by xcex3 when the angle xcex8 is xe2x80x9c0xe2x80x9d; a length between the axis of said crankshaft and said crankpin is represented by R; a length of the straight line connecting the axes of said rotary shafts and the axis of said movable eccentric shaft is represented by Rp; a rotational angular speed of said crankshaft is represented by xcfx89; and a ratio of the rotational speed of said movable eccentric shaft to the rotational speed of said crankshaft is represented by xcex7 and the rotational direction thereof is represented by xcex7=+0.5 or xcex7=xe2x88x920.5, the following equation is established:
L4xc2x7sin xcfx864xc2x7dxcfx864/dt+L2xc2x7cos (xcex1+xcfx861)xc2x7dxcfx861/dtxe2x88x92Rxc2x7xcfx89xc2x7sin xcex8=0
Wherein
xcfx864=arcsin {L2xc2x7cos (xcex1+xcfx861)+Rxc2x7sin xcex8xe2x88x92xcex4}/L4
dxcfx864/dt=xcfx89xc2x7[xe2x88x92L2xc2x7sin (xcex1+xcfx861)xc2x7{Rxc2x7cos (xcex8xe2x88x92xcfx863)xe2x88x92xcex7xc2x7Rpxc2x7cos (xcex8pxe2x88x92xcfx863)}/{L1xc2x7sin (xcfx861+xcfx863)}+Rxc2x7cos xcex8)]/(L4xc2x7cos xcfx864)
xcfx861=arcsin [(L32xe2x88x92L12xe2x88x92C2xe2x88x92D2)/{2xc2x7L1xc2x7(C2+D2)}]xe2x88x92arctan(C/D)
xcfx863=arcsin {(Rxc2x7cos xcex8xe2x88x92L6xe2x88x92Rpxc2x7cos xcex8p+L1xc2x7sin xcfx861)/L3}
C=L5+Rpxc2x7sin xcex8pxe2x88x92Rxc2x7sin xcex8
D=L6+Rpxc2x7cos xcex8pxe2x88x92Rxc2x7cos xcex8
xcex8p=xcex7xc2x7xcex8+xcex3
dxcfx861/dt=xcfx89xc2x7{Rxc2x7cos (xcex8xe2x88x92xcfx863)xe2x88x92xcex7Rpxc2x7cos (xcex8pxe2x88x92xcfx863)}/{L1xc2x7sin (xcfx861+xcfx863)}
and crank angles xcex8 at a top dead center at each of the intake and exhaust strokes and at the top dead center at the compression stroke are determined from said equation, and the length L1 of said second arm; the length L2 of said first arm; the length L3 of said control rod; the length L4 of said connecting rod; the length L5 from the axis of said crankshaft to the axes of said rotary shafts in the direction of the y-axis; the length L6 from the axis of said crankshaft to the axes of said rotary shafts in the direction of the x-axis; the amount xcex4 of offsetting of the cylinder axis from the axis of said crankshaft in the direction of the y-axis; the angle xcex1 formed by said first and second arms; the length R between the axis of said crankshaft and said crankpin; the length Rp of the straight line connecting the axes of said rotary shafts and the axis of said movable eccentric shaft and the angle xcex8p when the angle xcex8 is xe2x80x9c0xe2x80x9d, are determined so that the top dead center at each of the intake and exhaust strokes and the top dead center at the compression stroke are congruous with each other, according to the following equation:
X=L4xc2x7cos xcfx864+L2xc2x7sin (xcex1+xcfx861)+Rxc2x7cos xcex8
which represents a level X of the piston pin at both said crank angles xcex8.
The operation according to the configuration of the first feature will be described below with reference to FIG. 5 diagrammatically showing the arrangements of the piston pin, the connecting rod, the crankshaft, the crankpin, the first arm, the second arm, the control rod and the movable eccentric shaft. When the coordinates (Xpiv and Ypiv) of the movable eccentric shaft are determined, a moving speed (dX/dt) of the piston pin is determined by differentiating the position of the piston pin in the direction of the x-axis determined by {X=L4xc2x7cos xcfx864+L2xc2x7sin (xcex1+xcfx861)+Rxc2x7cos xcex8}, and an equation provided when dX/d=0 has four solutions in a range of xe2x88x922xcfx80 less than xcex8 less than 2xcfx80. The four solutions are associated with the motion of a 4-cycle engine, whereby crank angles providing a top dead center at a compression stroke, a top dead center at each of intake and exhaust strokes, a bottom dead center after an expansion stroke and a bottom dead center after the intake stroke are determined and used to determine various positions of the piston pin in the directions of the x-axis and the y-axis. When the position of the piston pin at the top dead center in the direction of the x-axis at compression stroke is represented by Xctdc; the position of the piston pin in the direction of the x-axis at the top dead center at each of the intake and exhaust strokes is represented by Xotdc; the position of the piston pin ion the direction of the x-axis at the bottom dead center after an expansion stroke is represented by Xebdc; and the position of the piston pin in the direction of the x-axis at the bottom dead center after the intake stroke is represented by Xibdc, a stroke Scomp at the compression stroke and a stroke Sexp at the compression stroke are represented by (Scomp=Xctdcxe2x88x92Xibdc) and (Sexp=Xotdcxe2x88x92Xebdc), respectively, and the length L1 of the second arm, the length L2 of the first arm, the length L3 of the control rod, the length L4 of the connecting rod, the length L5 from the axis of the crankshaft to the axes of the rotary shafts in the direction of the y-axis; the length L6 from the axis of the crankshaft to the axes of the rotary shafts in the direction of the x-axis; the amount xcex4 of offsetting of the cylinder axis from the axis of the crankshaft in the direction of the y-axis; the angle xcex1 formed by the first and second arms; the length R between the axis of the crankshaft and the crankpin; the length Rp of the straight line connecting the axes of the rotary shafts and the axis of the movable eccentric shaft and the angle xcex8p when the angle xcex8 is xe2x80x9c0xe2x80x9d, are determined so that Scomp less than Sexp is satisfied and Xctdc=Xotdc is satisfied. Thus, the stroke of the piston at the expansion stroke can be set larger than that at the compression stroke and in addition, the top dead center at each of the intake and exhaust strokes and the top dead center at the compression stroke can be set at the same level. As a result, it is possible to prevent the occurrence of the interference of each of an intake valve and an exhaust valve and a top of the piston with each other; to provide an enhancement in compression ratio in the engine to enable the operation at a higher thermal efficiency, and to achieve the sufficient scavenge by the piston and to prevent a reduction in output in a full-load state and the instability of burning in a lower-load state.
According to a second feature of the present invention, in addition to the first feature, a locus of movement of the piston pin is determined to be fallen into a range between the x-axis and one of tangent lines parallel to the x-axis and tangent to a locus described at the expansion stroke by a point of connection between the connecting rod and the first arm, which is closest to the x-axis. With such feature, it is possible to reduce the friction of the piston and suppress a piston slap sound. More specifically, when the piston is at the expansion stroke, a large load is applied to the piston, but if the change in attitude of the piston is increased due to the large load at that time, the friction is increased and the piston slap sound is magnified. However, the above-described determination of the locus of movement of the piston pin ensures that the connecting rod is always inclined to one side at the expansion stroke, notwithstanding that the piston receives the large load at the expansion stroke, whereby the change in attitude of the piston can be suppressed to reduce the friction of the piston and to suppress the generation of the piston slap sound.
According to a third feature of the present invention, in addition to the second feature, the range of the crank angle at the expansion stroke is set larger than that at the intake stroke, and the range of the crank angle at the exhaust stroke is set larger than that at the compression stroke. With such configuration, it is possible to avoid the degradation of inertia vibration due to an increase in acceleration of the piston. More specifically, during lowering of the piston, the stroke at the expansion stroke is larger than that at the intake stroke, and during lifting of the piston, the stroke at the exhaust stroke is larger than that at the compression stroke. In the setting in which the top and bottom dead centers are alternated with each other at the crank angle of 180 degrees, the speed of the piston at each of the expansion and exhaust strokes at which the stroke is larger is higher than that at each of the intake and compression strokes at which the stroke is smaller, and the acceleration of the piston is increased due to such a large difference between the speeds, thereby bringing about the degradation of inertia vibration. However, by setting the range of the crank angle at each of the expansion and exhaust strokes at which the stroke is larger at a value larger than the range of the crank angle at each of the intake and compression strokes at which the stroke is smaller, as described above, the speed of the piston at each of the stokes can be further uniform to suppress the variation in acceleration of the piston at the bottom dead center after the intake and expansion strokes and the variation in acceleration of the piston at the top dead center after the intake and expansion strokes to avoid the degradation of inertia vibration.
According to a fourth feature of the present invention, in addition to the third feature, the ranges of the crank angles at the expansion and exhaust strokes are set at values exceeding 180 degrees, respectively. With such configuration, the speed of the piston at each of the intake, compression, expansion and exhaust strokes can be further uniform to more effectively suppress the variation in acceleration of the piston at the bottom dead center after the intake and expansion strokes and the variation in acceleration of the piston at the top dead center after the intake and expansion strokes, thereby more effectively avoiding the degradation of inertia vibration.
According to a fifth feature of the present invention, in addition to any of the first to fourth features, the movable eccentric shaft is mounted on the rotary shafts having the axes disposed at locations spaced within the x-y plane apart from the axis of the crankshaft by the lengths L5 and L6 in the directions of the y-axis and the x-axis, respectively, so that it is displaced from the axes of the rotary shafts by a distance corresponding to a radius Rp, and wherein when the length R between the axis of the crankshaft and the crankpin is set at 1.0, the length L1 of the second arm is set in a range of 1.7 to 4.5; the length L2 of the first arm is set in a range of 0.6 to 5.2; the length L3 of the control rod is set in a range of 4.3 to 6.9; the length L5 between the axis of the crankshaft and the rotary shafts in the direction of the y-axis is set in a ranger of 2.3 to 4.0; the length L6 between the axis of the crankshaft and the rotary shafts in the direction of the x-axis is set in a range of 0.00 to 3.35; and the radius Rp is set in a range of 0.25 to 1.80, as well as the angle a formed by the first and second arms is set in a range of 105 to 180 degrees. With such configuration, it is possible to provide the configuration of the fourth feature, thereby more effectively avoiding the degradation of inertia vibration.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.